but when they are bad, how they treat you behind closed doors, trust me, it's worse than you can imagine. There's no limit to how low they will go to coerce you. Even when the relationship seems good, they'll probably have all these subtle games going on, like seducing your family members or something, but right up to the point where they can plausibly deny it. Getting off on having influence on people's emotions, while judging everyone for falling for it.
Dude, what the hell. I'm an INFJ and that's the kind of behaviour I wholeheartedly despise. (I'm not saying whatever you have gone through isn't true. It can be.)
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I can have strong emotional influence on people, but I would not use that ability "behind people's back" or "against people". I'd rather just curl up in my shell and remain mentally distant towards somebody - which isn't particularly nice behaviour either but not as bad - if there were a risk that I couldn't control myself and ended up doing something nasty.
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However, I can easily imagine how an INFJ might become a horrible emotional manipulator. The world isn't exactly fit for INFJs (as it isn't for many different kinds of people either, not trying to act too special here). Being very complex, INFJs growing up might be left without the support and reassurance they (as we all) need. This is a phenomenon I'm used to experiencing a lot.
E.g. I can be very excited about some thought in my head, but when I verbalize it to others, I can at best be not understood but at worst be horribly misunderstood. There was a time when I was a child and I used a metaphor in my communication, which a person a lot older than me (due to their age, I expected them to understand metaphors) took literally and thought I was off to kill somebody ... Hearing how they had interpreted my metaphoric language, it threw me to one of those "is this really happening" -moments when your head just goes numb and you don't know which step you should take next - or if you'd rather just disappear from the world right there. It's times like these when you think you can't interact with the world. There's a barrier that can't be exceeded.
Now, as AN ADULT, I'd know how to work a situation like that out and clear the misunderstanding. But I'm afraid, for some INFJs it takes even decades until they're brave enough to try and interact with the world again - not through a fake persona but as who they honestly are with all their wants and needs and such. Well, we're still people and people want to feel love and stuff. So those INFJs probably still seek relationships and end up using pretty cranky communication methods. It's not exactly right usually; even if it can be explained, it can't be justified.
(I started to follow a line of thought here that might have a lot of truth in it, but it also could be only a very narrow sector of all the possbile reasons behind an INFJ acting certain way.)
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I think stressing the INFJ personality type's "worse sides" is trending now, because the image of INFJs most MBTI information sources give is pretty flattering. An antithesis for the thesis. Hopefully we'll reach a synthesis somewhere in the future as well.
Just for comparison. The ENFP changing their values every other day and thus confusing people - maybe leaving their partner "just because they woke up one day and felt like it" - isn't considered particularly "evil" because the general perception on ENFPs acknowledges that trait. The ENTP stepping on people's shoes and arguing with people when the context would ask for not doing that is'nt either considered "evil" because that's also mentioned on the personality type descriptions. Even though both of those behaviours have a huge antisocial tone to them.
The INFJ descriptions maybe say "they can be overly secretive", but they definitely don't cover all the implications that might follow from being overly secretive. Like, the INFJ being secretive about their true feelings.
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Anyways, as I said, I can have a strong emotional influence on people. Related to that, I've enjoyed INTJs, ENTPs and INTPs company because I get the feeling that they don't really become confused by my emotional bombarding (I wish it was less bombarding and more something I could control, definitely working on that) as much as other types. They can "stand their ground", remain calm and think things through logically. But according to your post, INFJs can tremendously confuse and end up hurting INTPs as well. Maybe I have to reconsider my ideas.
It's so much text in here, sorry for kind of lashing out.